The present invention relates to a solenoid valve for controlling a fuel injector of an internal combustion engine.
Such a solenoid valve, as referred to in German Published Patent Application No. 196 50 865, may be used for the control of the fuel pressure in the control pressure chamber of a fuel injector, such as an injector of a common-rail fuel injection system. The fuel pressure in the control pressure chamber controls the movement of a valve plunger, by which an injection opening of the fuel injector may be opened or closed. The solenoid valve has an electromagnet positioned in a portion of the housing, a movable armature, and a control valve member, which is movable with the armature and acted upon by a closing spring in the closing direction. The closing spring cooperates with a valve seat of the solenoid valve and thereby controls the fuel outflow from the control pressure chamber. In the solenoid valve referred to in German Published Patent Application No. 196 50 865, the armature includes two parts, namely, an armature bolt and an armature plate slidingly supported on the armature bolt. Solenoid valves may also include single-part armatures for controlling fuel injectors, in which the armature bolt is firmly connected to the armature plate.
It is believed that these solenoid valves have disadvantageous armature bounce. When the magnet is switched off, the armature and the control valve member are accelerated toward the valve seat by the closing spring of the solenoid valve, to close a fuel outflow channel from the control pressure chamber. The bounce of the control valve member onto the valve seat may result in a disadvantageous vibration and/or bounce of the control valve member onto the valve seat. This may impair the control of the fuel injection process. In the solenoid valve referred to in German Published Patent Application No. 196 50 865, therefore, the armature plate is positioned movably on the armature bolt so that, upon the bouncing of the control valve member onto the valve seat, the armature plate moves counter to the tension force of a return spring. As a result, the effectively braked mass and thus the kinetic energy causing the bounce of the armature hitting the valve seat may be diminished. However, the armature plate may post-oscillate on the armature bolt after the closing of the solenoid valve, so that additional measures may be required for damping the undesired post-oscillation of the armature plate.
In an exemplary solenoid valve according to the present invention, a sliding element, which guides the armature, is positioned in the armature space of the solenoid valve, so that the armature space is subdivided into a pressure relief chamber connected to a fuel low-pressure connection and a hydraulic damping chamber, into which the fuel outflow channel opens from the control pressure chamber. The damping chamber is connected to the pressure relief chamber via at least one connecting channel equipped with a throttle.
When the solenoid valve is closed, the control valve member, in the damping chamber, moves toward the valve seat. This causes a rapid displacement of the fuel in the damping chamber, which may not immediately escape into the relief chamber through the throttle-equipped connecting channel. Thus, a fuel pressure cushion is formed, which opposes the motion of and brakes the control valve member together with the armature, so that the impulse transmitted onto the valve seat by the striking of the valve seat by the control valve member is reduced. This permits reduction of the armature bounce (or the bouncing movement of the control valve member on the valve seat). Therefore, by the use of an exemplary solenoid valve according to the present invention, shorter intervals may be set between pre-injection, main injection and post-injection, since the armature requires less time for achieving a defined neutral position. This also applies for solenoid valves, in which the armature plate is formed as one piece with the armature bolt. One-piece armatures may be manufactured with less effort and may reduce costs.
When the solenoid valve is open, the fuel flowing out of the fuel outflow channel of the control pressure chamber first flows into the damping chamber. Due to the throttling of the fuel flow from the damping chamber into the pressure relief chamber, a defined pressure pattern in the pressure relief chamber is ensured, or at least made more probable. This may positively effect the motion of the armature in the pressure relief chamber, and thus the course of the injection procedure. A pressure surge, which may form in the control pressure chamber when the fuel discharge channel is opened, does not directly reach the pressure relief chamber, but rather, first reaches the damping chamber. Only after reaching the damping chamber, does the pressure surge reach the pressure relief chamber via the connecting channel equipped with the throttle. Quantitative deviations between individual injection processes may be advantageously decreased by the division of the armature chamber.
Furthermore, the pressure cushion generated in the damping chamber may reduce the seat loading of the valve seat at high closing forces.
It is believed to be advantageous to adjust the volume of the damping chamber and the at least one throttle to one another, so that an approximately constant fuel pressure is established in the damping chamber after a relaxation period, after the opening of the solenoid valve.
The sliding piece includes a sliding sleeve guiding the armature and a flange region, forming a separating wall between the damping chamber and the pressure relief chamber. This stationarily holds the sliding piece in the armature chamber. By this measure, a defined volume of the damping chamber may be simply set.
It is believed to be advantageous to design the at least one connecting channel as a feed-through opening furnished with a throttle in the flange region of the sliding piece, since it may be easy to manufacture the connecting channel in the sliding piece. Since the at least one feed-through opening is positioned inside the projection of the armature plate in the direction of motion of the armature, the fuel flowing from the damping chamber into the pressure relief chamber may flow against the armature plate, which may support the braking procedure of the armature.
Since the sliding sleeve guiding the armature projects away from the flange of the sliding piece toward the valve seat, a sufficiently dimensioned damping chamber may be formed between the sliding sleeve and the housing of the solenoid valve.
In another exemplary embodiment according to the present invention, the throttle section of the at least one connecting channel is formed by a slit in an end face of a valve piece set into the housing of the fuel injector facing the damping chamber and furnished with the valve seat, the slit being covered by a support part partially bordering on the damping chamber.
The support part may be, for instance, a screw member holding the valve piece in the housing.
A section of the connecting channel, which connects the damping chamber to the pressure relief chamber, may be formed by a leakage channel situated inside the housing of the fuel injector.